1. Field of the Invention
The present invention generally relates to positive-displacement pumps, and more particularly to positive-displacement pumps that include an auxiliary pumping system that provides an auxiliary stream of the pumped fluid.
2. Discussion of the Prior Art
In many pumping applications, it is desirable to have an auxiliary stream of the pumped fluid to provide cooling and/or lubrication within a pump. Such an auxiliary stream may be used for cooling and/or lubrication of dynamic seals, whether packing or mechanical face seals, or of bearings or bushings, or cooling within separation canisters in magnetically-coupled pumps. However, it is common for such pumping systems to have the auxiliary stream driven by differential pressure.
Systems using differential pressure include a passageway between two locations within a pump. For instance, the pressure is higher in the first location than in the second location. Thus, it may simply be a passageway through a pump casing with the first location being in the pumping chamber behind the rotor, where the pressure is relatively high, while the second location is in the suction port chamber, where the pressure is relatively lower. Alternative systems can be much more complex and include several apertures, grooves, tubes and/or other passageways through multiple pump components, whether entirely within or even running externally of the pump casing.
The prior art auxiliary pumping systems that use differential pressure to move the fluid suffer from numerous disadvantages. The flowrate in such systems is strongly dependent on the differential pressure of the pump. Thus, the flowrate is very low when the differential pressure is very low, even though often the need for fluid flow for cooling or lubrication does not diminish with reduced differential pressure. Similarly, the flowrate of these auxiliary systems is strongly dependent on the viscosity of the pumped fluid. Therefore, the flowrate is very low when the viscosity is high, even though the need for fluid flow for cooling or lubrication does not diminish with increased viscosity. The differential pressure systems also are prone to clogging if the fluid contains solids or accumulations of thickened fluid. Clogging can completely disable the function of the auxiliary pumping stream.
There is at least one prior art system that utilizes an oscillating displacement system that does not produce continuous flow. The system is used in an internal gear pump, with a hole in the idler gear, in a root area between teeth. During most of the angle of rotation of the idler gear, the hole is exposed to either suction or discharge pressure and flow can move based on differential pressure, similar to the movement in the above-mentioned prior art devices. However, when the rotor and idler teeth mesh, they close off the chamber and compress it, and during this short time, flow is forced into the hole in a positive-displacement manner. The oscillation occurs because when the teeth begin to unmesh, the chamber expands and pulls fluid back out of the hole, thus momentarily reversing the flow.
Such oscillating systems include disadvantages. The oscillating nature of the system means that the same fluid is moved back and forth, with less new fluid being introduced. As such, these systems do not have the capacity to produce significant cooling effects. Compounding this problem, the rapid oscillation also only moves a very small volume of fluid per displacement.
The present invention addresses shortcomings in prior art pumping systems, while providing positive-displacement auxiliary pumping systems that provide an auxiliary pumping stream for use in enhanced cooling and/or lubrication.